المواد الملونة ومواد الطلاء السميك ١_a , من كتاب تكنولوجيا التصوير , د.م محمد حماد

- Colored materials and thick coating materials

.. This is its color and the stability of this color in light and heat, and when some air pollutants (hydrogen sulfide) are present (2) in particular, the factors that can spoil the color with their effects.

The characteristics that must be taken into account when using colored materials (dyes) or any such material are the following:

Characteristics of granules of colored materials... The shape of the granules is usually spherical and rarely in the form of sheets or needles, and the dimensions of the granules, their average diameter and the distribution of their granules, are what affect the speed of their deposition in the liquid paint, their ability to color, their resistance to light leakage, their mixing with oil, And it may have protective properties.

Its density affects the rate of sedimentation.

Its ability to color and its ability to prevent the deposition of light inside.

Mixing it with oil (the weight of linseed oil required for mixing with one hundred grams of dye) forms a very thin lining on the surface (consisting of one part), which is a property that allows determining the composition of the powder paste and affects the accuracy of the dye distribution on the surface, and therefore the fluidity properties of the paint and the optical properties of the paint after it has dried.

Its solubility in water or in organic liquids, and its sensitivity to acids and alkalis

And we will explain in the following the dyes or colored materials, and to clarify the resistance and not being affected by light and air, we put stars in front of each color with a number of 4 **** for the colors that are not affected, and with a number of 3 *** for the high-resistance colors, and with a number of 2 ** for the medium-resistant colors, and with a number of 1 For low-resistance colours

(I) Mineral Dyes and Other Coatings:

As a result of the diversity of the chemical composition of the colored materials, these dyes are classified according to their color
Imaging Technology -
White dyes:

The four main dyes whose consumption is of great importance are: silver white, zinc white, lenophone white (a mixture of barium sulfate and zinc sulfide), and titanium white, which was known in the color industry and was used recently.

(1) Bianco d'Argento silvery white: This color is also known as lead white (Bianco di Piombo) cherose (because it is prepared in industry by virtual oxidation of lead (in thin sheets or powder) and then melts the crust of litharge (mertic) or lead hydroxide and (Aid (2) in acetic acid in the form of lead acetate base, which turns to lead white (silver white) by the effect of carbon dioxide. It is an easy-to-dissolve dye due to its weak mixing with oil (12 to 13 /). However, like all lead dyes, it prevails at Exposing it to a sulfuric atmosphere turns it into lead sulfide.In addition, it is a pigment with a basic reaction that is incompatible with liquids whose acidity does not exceed 10, as it contains lead soap, which causes the liquid paint to be mistaken.But as a result of this property, it is a pigment that prevents rust and is compatible with oil and varnishes. After using the paint, lead white (silver white) combines slowly with free fatty acids and increases its flexibility and viscosity and prevents water leakage from it. Roofing for buildings and painting for ship divers to prevent rust. But because it is a toxic substance that poisons wounds and causes what is known as lead paralysis (lead hemiplegia) ... its use is prohibited in France in all building paints.

This color is very undesirable in photography due to the speed of its color change, due to the abundance of lead sulfur in it. This phenomenon can be seen in old pictures in which the painter used silver white alone, so we see that the color tends to be black, yellow or red at times. Therefore, another color must be used in the parts where white is intended to appear bright or mixed with it.

Although silver-white is characterized by its rapid drying, as it dries in six days if used purely... However, it loses this feature when mixed with another color, and follows the speed of drying of the color mixed with it. When using this color, it should be noted that it is suitable for mixing with all fixed colors to obtain various shades of a warm color, but it does not accept mixing with sulfuric compounds such as vermilion red, frilly, ultramarine blue, and cadmio yellow, and it is not placed in gaseous places such as toilets and acid factories because it changes and darkens. But to restore its original color, it is washed with oxygen water. And to detect his cheating, a little bit of it is added to the diluted Azotic acid, and it dissolves in it if it is pure, even if it is mixed with oil. If heated in the open air with extreme heat, it turns into yellow lead dioxide. We repeat here that it must be noted that this color is a toxic substance and we must be careful not to be contaminated with it or drink from the body or inhale its volatile atoms in the air.
Bianco di zinco (B) White Renk *** It is made by the acidification of the country Blende with the powder of evaporated zinc at a temperature of 1000 C, so it turns into white smoke, and as soon as it touches the air it becomes ash and falls off in small pieces like white cotton that contains zinc. It is a pigment of varying whiteness and accuracy, less light than lead white, but it does not blacken in the sulfur atmosphere. It has a basic reaction that is not compatible with acidic resins, but it is used in oil paints and fatty varnishes, where it replaces acidage, because it is not harmful to health and its moderate price. To reduce its fragility, zinc white is usually mixed with litophone (only in interior paints) or with titanium white.

And you notice that zinc white is faster in external atmospheres than silvery white... And since the pictures are naturally placed inside the dwellings... or in closed places far from the open air, so the zinc white has an advantage that compensates for that deficiency, which is its strong endurance and non-transformation Its color is the effect of daylight. Also, Renk white does not affect the essence of colors with a stable tint when mixed with it.

It has been proven that zinc white gives a pure effect, and therefore it is desirable to use it in bright places, such as reflections of light in the sky, the colors of transparent sea waves, bright flowers, and other things that need care to display them in fresh, delicate colors.

Zinc white is slow drying, as it dries in twenty days if used purely, but it is affected by the speed of drying of the colors with which it is mixed. And the adulterated sample of it is detected by putting a quantity of it in a tester with sulfuric acid, then heating it... If it all melts, it indicates purity. : color knows

(c) Linobon white *** Bianco lithopone

By the name of the fixed white Bianco permanente because its color is almost constant. And its chemical composition is (Cb + Bacb ((4). It is a mixture consisting of a molecule of zinc sulfide and a part of barium sulfate that precipitate together as a result of the interaction of zinc sulfate in an aqueous solution of barium sulfide. It is a fine-grained dye to a large and homogeneous degree and does not prevail in the sulfuric atmosphere. Its ability to prevent light is similar to that of zinc white, and it is chemically inert, but it is rarely used except in interior paints due to its tendency to disintegrate in bad weather. There is another compound similar to lithopone, which is lycopone. leucopone

It is manufactured and used in Germany a lot (d) white titanium **** Bianco di titano, which is titanium dioxide (T (21) and is made by the effect of acids on ilmenite) which is natural iron titanate) (T (41)

Titan was known when it was found on the surface of the earth. It is composed of titanium dioxide in the form of a natural clay substance, and it is extracted from mines located in many parts, but its mines in Italy are characterized by abundance and are more pure.